The present invention relates to lasers, and more particularly to a laser transmitter for communication of signals across a fiber optic network, such as a cable television network.
A cable television network is primarily designed to distribute television signals from a "headend" to the homes of individual subscribers. In the past, cable television networks have utilized coaxial cable comprising an inner conductor and a conductive outer shield. At the present time, a new technology is evolving wherein cable television signals are transmitted over fiber optic cables. In fiber optic systems, light from a laser is modulated with a radio frequency (RF) television signal for transmission across a fiber optic cable. An example of a cable television system in which optical fibers connect the headend to a switching point from which the signal is connected to a subscriber's home, is provided in U.S. Pat. No. 4,621,282 to Ahern, entitled "Transmitting Stereo Audio Programs in Cable TV Systems". In the system of that patent, signals are transmitted over the fiber optic cable in digital as opposed to analog form.
In implementing a cable television network utilizing fiber optic technology and laser transmitters, replaceable laser modules may be used. If a laser module burns out, or otherwise becomes inoperable, it can be replaced in the field by substituting a new laser module therefor. A problem arises, however, in that different laser modules have different characteristics. Alignment of a transmitter in the field upon replacement of a laser module can be complicated and time consuming.
It would be advantageous to have a laser module that can be replaced in the field, with minimum effort, and no need for time consuming alignment to compensate for the specific characteristics of the new laser module. It would be further advantageous to provide a laser transmitter which adjusts itself upon the installation of a new laser module, to compensate for the characteristics of the module.
The present invention relates to such a laser transmitter and to a method for aligning a laser transmitter to provide proper modulation of a signal for fiber optic communication.